1. Field of the Invention
The present invention relates to a scanning irradiation device of a charged particle beam, in which a charged particle beam emitted from an accelerator is deflected by a first scanning electromagnet and a second scanning electromagnet and is irradiated to an irradiation target.
2. Description of the Related Art
A scanning irradiation device of a charged particle beam in known particle beam therapy systems includes an accelerator which emits a charged particle beam (for example, beam of electron, proton, and heavy ion); a group of electromagnets such as quadrupole electromagnets and deflection electromagnets which transport abeam taken out from the accelerator; two scanning electromagnets (scanning electromagnet pair) in which beam deflection surfaces are located on the same surface, and excited in opposite polarity to each other; a magnet rotation driving mechanism which rotates the scanning electromagnet pair around an incident beam axis; a range shifter which degrades beam energy and stops a beam at any depth in the inside of the body by taking in and out a plurality sheets of plates made of a material such as polyethylene or the like having density equivalent to water and being different in thickness on the incident beam axis; a scanning irradiation control device which performs control of the scanning electromagnet pair and the range shifter; a recumbent position treatment bed which is a flat bed; and a treatment bed driving mechanism which moves the recumbent position treatment bed to any position. Further, the scanning irradiation device of the charged particle beam is composed of a rotational structure (rotating gantry) mounted with the group of electromagnets which transport the beam, the scanning electromagnet pair, the magnet rotation driving mechanism, the range shifter, and the scanning irradiation control device; and a gantry rotating mechanism which determines an irradiation direction to an irradiation target.
Next, the operation will be described. A patient is mounted on the recumbent position treatment bed, the patient is moved to any position by the treatment bed driving mechanism, and the patient's position is adjusted so as to correctly irradiate a beam to the irradiation target. The beam taken out from the accelerator is deflected by the scanning electromagnet on the upper stream side to a direction deviating from the incident beam axis, deflected in an opposite direction by the scanning electromagnet on the lower stream side, and finally, irradiated to the irradiation target parallel to the incident beam axis. Two scanning electromagnets on the upper stream side and the lower stream side are integrated and rotated at any angle around the incident beam axis; and therefore, the beam is distributed and irradiated to the irradiation target in any shape of two-dimensional flat surface.
Next, the range shifter takes in and out the plurality of the plates having the density equivalent to water and being different in thickness; and accordingly, energy of the beam is attenuated to any energy, depth at which the beam is stopped is changed, similarly the beam is distributed in any shape of two-dimensional flat surface, and the beam is irradiated. As described above, a spot of the beam is three-dimensionally arranged; and accordingly, irradiation is performed to the irradiation target in a uniform radiation dose distribution in accordance with its three-dimensional shape. In the scanning irradiation control device, the aforementioned series of movements is controlled so that the respective apparatuses operate in cooperation.
When important organs which do not have to be irradiated are located in the vicinity of the irradiation target, there is a difficult case to give sufficient radiation dose to the irradiation target by only irradiation from one direction while suppressing the radiation dose to the important organs. In this case, the group of electromagnets which transport the beam, the scanning electromagnet pair, and the range shifter are integrated to the rotational structure (rotating gantry), and the rotating gantry is rotated; and accordingly, irradiation (referred to as multiple field irradiation) is performed from a plurality of arbitrary angle directions so as to avoid the irradiation to the important organs. Incidentally, as a known art related to the aforementioned scanning irradiation device of the charged particle beam, there are the following patent documents: Japanese Unexamined Patent Publication No. 10-263098, Japanese Unexamined Patent Publication No. 11-309220, and Japanese Unexamined Patent Publication No. 2002-113118. In the case of performing the multiple field irradiation in order to suppress radiation dose to the important organs to be low, the known scanning irradiation device of the charged particle beam needs the rotating gantry which integrally rotates with beam line apparatuses such as the group of electromagnets of the quadrupole electromagnets, the deflection electromagnets, and the like, which transport the beam; the scanning electromagnets; and the range shifter. The rotating gantry is of the rotational structure having a diameter of approximately 10 m; and therefore, the rotating gantry becomes an expensive irradiation device.